The present invention relates to an optical component comprising an optical waveguide and positioning markers which are formed on a quartz glass substrate for applications such as an optical transmission/reception module in the field of optical communication, and a method for making the same.
In an optical transmission/reception module for optical communication, the quality of connection, in particular the accuracy of optical path alignment, between the optical fiber and the optical device such as a photodiode and laser diode on the substrate dictates the performance of the module. Also, in such an optical transmission/reception module for optical communication, typically, the optical fiber is connected to the optical device via an optical waveguide, instead of connecting them directly to each other. Therefore, the substrate on which the waveguide is formed includes a marker, typically on each of the four corners of the substrate, to properly position it with respect to the optical device or the optical fiber.
As can be readily appreciated, the positioning marker is required to be properly positioned with respect to the optical waveguide at a high precision. Conventionally, the optical waveguide and positioning markers were formed in separate steps, and the positioning of the patterning mask was required to be performed at a high precision in these two separate steps. This required a high level of expertise, a complex work process, and expensive equipment such as a photographic exposure device.
During the fabrication process of such an optical transmission/reception module, a thermal processing step is typically conducted primarily for removing voids and internal stresses which tend to develop in stepped portions when forming the clad layer. Because the materials for forming the optical waveguide (such as the glass that is used for forming the clad layer) and the material used for forming the positioning marker (such as metal) have different thermal expansion coefficients, cracks may be generated between them depending on the shape of the positioning marker. This may affect the reliability of the component, and may reduce the yield of the production process.
In view of such problems of the prior art, a primary object of the present invention is to facilitate the fabrication of an optical component comprising an optical waveguide and positioning marker on a same quartz or silicon substrate.
A second object of the present invention is to improve the reliability of such an optical component, and increase the yield of the fabrication process for such an optical component.
A third object of the present invention is to allow a positioning marker to be formed in such an optical component both accurately and economically.
According to the present invention, such objects can be accomplished by providing a method for making an optical component comprising an optical waveguide and positioning marker which are formed on a common substrate, comprising the steps of: forming a lower clad layer on the substrate; forming a core layer having a refractive index different from that of the lower clad layer over the lower clad layer; patterning the core layer into a core segment having a prescribed shape; forming an upper clad layer having a similar refractive index as the lower clad layer over the lower clad layer and core segment; and forming a positioning marker on the substrate, the step of forming a positioning marker including the step of patterning a layer on the substrate so as to define the position of the positioning marker on the substrate; the patterning of the core segment and positioning marker being carried out by using a common mask.
This method provides an optical component comprising an optical waveguide and positioning marker which are formed on a common substrate, comprising: a substrate; a lower clad layer formed on the substrate; a patterned core segment having a refractive index different from that of the lower clad layer, and formed over the lower clad layer; an upper clad layer having a similar refractive index as the lower clad layer formed over the lower clad layer and core segment; and a positioning marker comprising a metallized patch placed over a layer on a same layer level as the core segment. Because the core segment and positioning marker are patterned by using a common mask, the positional relationship between the core segment and positioning marker can be established both accurately and simply.
To ensure a high level of recognizability, the step of forming the positioning marker may comprise the step of forming a metallized layer over the core layer so that the positioning marker may comprise a land region conformally underlying the metallized patch, and disposed on a same layer level as the core segment.
Such a structure can be easily realized if the step of patterning the core segment and positioning marker includes the steps of forming a photoresist layer, patterning the photoresist layer by using the common mask, and selectively removing the metallized layer and the core layer by etching.
If the step of patterning the positioning marker includes the step of forming an annular groove surrounding the positioning marker, the outer periphery of the positioning marker can be distinctly defined. If the annular groove is in turn surrounded by a layer which is on a same layer level as the core segment, the outer surface of the part of the outer clad layer near the positioning marker can be easily defined as a flat surface so that a favorable reference surface can be made available when mounting the optical component on a base.
To avoid creation of excessive stress concentration and/or thermal stress in the positioning marker, the positioning marker may be provided with rounded corners or a curved profile. If the substrate consists of substantially transparent material such as quartz glass, the positioning marker can be recognized from the reverse surface of the substrate, and this facilitates the positioning of the optical component when mounting it on a base.